Introduction

is a well-defined, spiral-shaped, gram-negative bacterium that is the primary causative agent of several gastric pathologies ranging from mild gastritis to gastric malignancies1. Infection with causes the chronic inflammation of the gastric mucosa and significantly increases the risk of developing duodenal and gastric ulcers as well as gastric cancer. The prevalence of infection varies widely depending on geography, age, race, ethnicity, and socioeconomic status. In developing countries, the rates appear to be greater than in developed countries with the majority of infections occurring during childhood. The prevalence among middle-aged adults is over 80% in many developing countries compared to 20% to 50% in industrialized countries2.

Similar to other developing countries, the rate of infection is notably high in Bangladesh. In 1997, Ahmad . reported that the prevalence of infection in Bangladesh was 92% in their serology-based study3. Mahalanabis ., in a study based on the 13C-urea breath test, also reported that the prevalence of was 84% in children aged 6-9 years old4. The overall prevalence in other Asian countries, including India (79% by ELISA) and Pakistan (84% by PCR), was also reported to be high3, 5. A significantly lower prevalence rate of was observed in Europe (40%) and the United States (40%)6, 7. High infection rates in developing countries may be the consequence of poor socioeconomic conditions and unhygienic lifestyles8.

The association between and gastroduodenal diseases necessitates the proper and timely diagnosis of infection in dyspeptic patients. Serology is quick, relatively inexpensive, and has good sensitivity. However, anti- IgG can usually be detected by 3-4 weeks after infection. This is a drawback since this mode of testing is ineffective at detecting the presence of during an earlier stage of pathogenesis9. Hence, the serology test results can be misleading and serve as false positive test results, which could be invalid10. The urea breath test provides a reliable, non-invasive method for the detection of infection. It has a high accuracy and reproducibility with a sensitivity and specificity of 90-96% and 88-98%, respectively11. Nevertheless, it is relatively expensive and requires mass spectrometric analysis, which may not be available in limited resource centers12.

also appears in stool as it is a gastrointestinal pathogen. Stool tests have the advantage of being non-invasive, and the specimen is easily obtainable. The monoclonal antibody-based stool antigen (HpSAg) assay has been clinically useful with a sensitivity and specificity of more than 90%. The specimen is easily obtainable and can be used as a routine diagnostic tool for infection because it seems to overcome the limitations of conventional invasive techniques3, 13. The detection of antigens in fecal samples may be useful for the non-invasive diagnosis of infection in both children and adults, selecting cases requiring endoscopic examination and in epidemiological studies14.

The present study was designed to analyze the diagnostic value of a rapid immunochromatography-based stool antigen test compared to invasive tests – like the rapid urease test and the histopathological analysis of a gastric mucosal biopsy – to diagnose infection in adult patients with peptic ulcer disease before treatment. For a developing country such as Bangladesh, the accessibility and reliability of rapid immunochromatography-based stool antigen tests can be useful in the quicker detection of infection, when obtaining valid results during and post infection, when overcoming the economic and technical barriers of other biochemical assays, and when facilitating proper disease management.

MATERIALS AND METHODS

Data analysis

All relevant medical history, physical examination records, clinical findings, and laboratory records of every subject were systematically added to a predesigned datasheet for subsequent analysis. The continuous variables were reported as the mean ± SD, and the categorical variables were reported as percentages. The two tests for the categorical data were used to compare the baseline characteristics. The statistical significance was defined as p <0.05, and the confidence interval was set at the 95% level. The SPSS (Statistical Package for Social Science) version 20 software was used for the analyses.

Characteristics	N = 140 (%)	Ulcer & erosion; n = 75 (53.6%)	No ulcer/erosion; n = 65 (46.4%)	Chi-square	P-value
Age (years); Mean age = 39.4 ± 11.4 (SD)
< 20	4 (2.9%)	2 (50.0%)	2 (50.0%)	15.4	0.0015
21 - 40	77 (55.0%)	52 (67.5%)	25 (32.5%)
41 - 60	48 (34.3%)	19 (39.6%)	29 (60.4%)
> 60	11 (7.8%)	2 (18.2%)	9 (81.8%)
Gender; male: female ratio of 1.06:1
Male	76 (54.3%)	43 (56.6%)	33 (43.4%)	0.6	0.4368
Female	64 (45.7%)	32 (50.0%)	32 (50.0%)

RESULTS

Clinical characteristics of the patients

Table 1 represents the age distribution of the patients with dyspepsia based on the endoscopic diagnosis. Among the 140 patients, 77 (55.0%) were in the 21- to 40-year-old age group, 48 (34.3%) belonged to the 41- to 60-year-old age group, 11 (7.8%) were in the age group above 60 years, and four (2.9%) were in the age group below 20 years old. The endoscopic diagnosis revealed that most of the patients (55.0%) with dyspepsia were in the age group of 21 to 40 years, followed by 48 (34.3%) in the age group of 41 to 60 below 20 years. The mean age of the patients was 39.4 ± 11.4 years. There were 76 (54.3%) male participants and 64 (45.7%) female participants in the study. The male:female ratio was 1.06:1, and no correlation was observed between the endoscopic findings and the sex of the patients. Among the different categories of peptic ulcer, antral erosion (25.7%) and prepyloric erosion (15.0%) were more prevalent (Figure 1A) (). The proportion of antral erosion was 57.4% in patients who were younger than 40 years old. This particular type of ulcer decreased to 23.4% in patients over 40 years. Patients over 40 years of age mostly suffered from pyloric erosion (42.9%) (Figure 1B). The percentage of reflux esophagitis in non-ulcer patients over 40 years of age increased by approximately 10% compared to those under 40 years of age (Figure 1C).

	No. of cases	Microscopic grading of curved bacilli			No Bacilli seen
		Grade 1	Grade 2	Grade 3	Grade 0
Histopathological grading of chronic gastritis
Mild	59	25	23	6	5
Moderate	14	2	9	3	0
Chronic active	2	0	1	1	0
Total	75	27	33	10	5
Rapid urease test (RUT)
Positive	67	24	33	10	0
Negative	8	3	0	0	5
Total	75	27	33	10	5

H. pylori status	Number of Patients	HpSAg Test Positive (%)	HpSAg Test Negative (%)	Chi2 and p-value
Positive	67	64 (95.5%)	3 (4.5%)	Chi2 = 6.47 p-value = 0.041
Negative	5	0 (0.0%)	5 (100%)
Indeterminate	3	1 (33.3%)	2 (66.7%)
Total	75	65	10

HpSAg Test	Case	Control	Total
Positive	64	4	68
Negative	3	16	19
Total	67	20	87

DISCUSSION

In this study, out of the 140 patients with upper GIT symptoms, the highest incidence (55%) was observed in the 21-40 year age group, followed by the 41-60 year (34.3%) age group (Table 1). The patients' ages ranged from 18 to 70 years, with a mean age of 39.4 years. A similar result was reported by Islam . (2010) in Dhaka, Bangladesh, where 60% of cases were within the 21 – 40 year age group, followed by 27% of cases in the 41 – 60 year age group16. Overall, the findings of the endoscopy were 30% normal, 16.4% reflux esophagitis, 25.7% antral erosion, 15% erosion in body and fundus, 5% gastric ulcers, and 6.43% duodenal ulcers (Figure 1A). These findings are similar to those of Ghosh . (2013) in Dhaka, Bangladesh, where among the 72 dyspeptic patients, the gastro-duodenal mucosa was normal in 55.6%. Additionally, there was reflux esophagitis in 8.3%, gastric erosion in 22.2%, gastric ulcers in 2.8%, and duodenal ulcers in 5.7% of patients17. Minor variations can be attributed to the differences in the exclusion and inclusion criteria used in both studies, as well as the socioeconomic level differences, and attitudes about seeking healthcare. In terms of the histopathology, chronic inflammatory infiltrates were seen in almost all patients, with the majority (78%) showing only mild inflammation (Figure 3A). The density of colonization increased with the severity of chronic inflammation in this study (Table 2). These findings were compatible with the study performed by Garg . (2012) in India, who reported that 70% of cases had a mild inflammation18. A greater density of organisms was noted in higher grades of inflammation. The concentration did not affect the activity and overall histological grading of chronic gastritis in their study. This dissimilarity may be due to the genetic differences, nutritional habits, and environmental factors between the two study populations19.

Alam . (2014) reported an 88.8% RUT positivity among the PUD patients in Dhaka. These findings are consistent with those of the present study15. In contrast to the present study, Islam . (2013) reported a lower RUT positivity (61.7% of patients were RUT positive and 38.3% were RUT negative). This dissimilarity may be because the sensitivity can vary with the site chosen for the biopsy due to the bacteria's patchy distribution. This means that a false negative test can occur due to sampling errors20. In this study, 89.3% (67/75) of the cases were rapid urease tested and histopathologically positive for (Figure 3C). This is in accordance with the studies performed by Islam . (2010) and Alam (2014) in Bangladesh, who reported that 79.0% and 87.6% of cases were infected by , respectively, using the same definition15, 16. In contrast, Korkmaz . (2015) found there to be a lower detection rate of -positive cases (50.6%) in Turkey21. The higher detection rate is not abnormal, as the study was conducted in a developing country where 80% — 90% of the population is estimated to be a carrier of this pathogen. The lower detection rate in the above study was probably due to the study being performed in a developed country.

Our study's most important finding was that the new HpSAg test showed excellent sensitivity and specificity. The sensitivity, specificity, PPV, NPV, and diagnostic accuracy of the HpSAg test were 95%, 80%, 94%, 84%, and 91%, respectively (Table 4). Several studies on monoclonal stool antigen tests based on the immunochromatography in various regions of the world have shown comparable results. A similar study performed in Malaysia showed a sensitivity, specificity, PPV, NPV, and accuracy of 91.7%, 100%, 100%, 94.6%, and 96.6%, respectively22. In addition, a study performed in Korea found the sensitivity, specificity, PPV, NPV, and accuracy of the stool immunochromatographic antigen assay (S-ICT test) to be 84.5%, 96.2%, 95.6%, 86.4%, and 90.4%, respectively23. However, these results differ from the findings of a study performed in Turkey by Korkmaz . (2015)21. They reported the sensitivity, specificity, PPV, NPV, and accuracy of an immunochromatographic HpSAg test as 51.6%, 96%, 88.8%, 76.1% and 79%, respectively. Lower sensitivities for HpSAg tests have occurred in special circumstances, such as those undergoing proton pump inhibitor (PPI) or bismuth therapy, patients with liver cirrhosis, and patients with hidden gastrointestinal bleeding23 which may have resulted in a false-negative HpSAg test. Nonetheless, the low colonization of bacteria in the stomach and the consequent low concentrations of antigen in the feces could be sufficient enough to cause false-negative results21.

CONCLUSION

TheHpSAg test can be a reliable alternative to the other techniques used to diagnose active infection. This test can also be utilized in some special circumstances, such as when an endoscopy is not available. However, due to the limited number of patients in this study, a larger investigation with a larger number of peptic ulcer patients is required to support the conclusions of this study. Overall, the HpSAg test is a sustainable alternative to invasive tests for the detection of infection in children, especially in developing countries such as Bangladesh where the prevalence of infection is very high. The test may also be used to monitor the therapeutic response to infection.

Abbreviations

CMCH: Chattogram Medical College and Hospital

GI: Gastrointestinal

HpSAg: Stool Antigen

ICT: Immunochromatograpic Test

MD: Microscopic Detection

NPV: Negative Predictive Value

PPV: Positive Predictive Value

PUD: Peptic Ulcer Disease

RUT: Rapid Urease Test

Acknowledgments

Department of Microbiology and Virology, Chittagong Medical College, Chattogram, Bangladesh.

Author’s contributions

Afreen Sultana: Study design, data collection, data analysis, data visualization, manuscript writing; Shakeel Ahmed: Supervision; Ershad Uddin Ahmed: Study design, supervision; Abul Faisal MD. Nuruddin Chowdhury: Study design, data analysis; Abul Kalam: Data collection; Arifur Rahman: Data collection; Farhana Akter: Manuscript writing and editing; A. H. M. Saiful Karim Chowdhury: Data collection; Sabrina Sharmin: Data collection; Jannatul Ferdous Mustry: Data collection; Ayan Saha: Study design, supervision, data analysis, data visualization. All authors read and approved the final manuscript.

Funding

None.

Availability of data and materials

Data and materials used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Ethics approval and consent to participate

This study was conducted in accordance with the amended Declaration of Helsinki. The Ethical committee of Chittagong medical college approved (Ref: CMC/PG/2018/379) the study, and all participants provided written informed consent.

Consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.